The present invention relates to novel asymmetric silicon-bridged metallocenes useful as catalysts for the polymerization of xcex1-olefins. It relates more specifically to novel silicon-bridged metallocenes containing fluorenyl and indenyl fragments and to a process for their preparation. Finally it relates to a process for polymerization of xcex1-olefins by using said asymmetric silicon-bridged metallocenes.
Some asymmetric silicon-bridged metallocenes derived from group 4 metals and containing fluorenyl and indenyl fragments have already been proposed for the polymerization of xcex1-olefins such as ethylene and propylene. For example, EP-A-0 754 698 discloses specifically dimethyl- or diphenyl-silylene (9-fluorenyl)-(2-methyl-1-indenyl)zirconium dichloride, dimethylsilylene (9-fluorenyl)-(2-methyl-4-phenyl-1-indenyl)zirconium dichloride, dimethylsilylene (9-fluorenyl)-(3-methyl-1-indenyl)zirconium dichloride and dimethylsilylene (9-fluorenyl)-(2-methyl-4-i-propyl-7-methyl-1-indenyl)zirconium dichloride in combination with aluminoxanes (MAO) for the polymerization of these xcex1-olefins. However the productivity of such silicon-bridged metallocenes remains insufficient and they do not lead to polymers having optimal properties.
Silicon-bridged indenyl fluorenyl metallocenes are generally produced by processes involving the addition of the indenyl anion to the (9-fluorenyl) silylhalide (J. Organomet. Chem., 1995, 497, 1). The application of this known route to substituted indenyl compounds does not provide satisfactory results presumably due to unfavorable steric hindrance of the indenyl compound.
It is an object of the present invention to solve the above problems by providing novel metallocenes useful as catalysts for olefin polymerization which are, in particular, able to produce with a particularly high activity polyethylene having high molecular weight. It is another objective of the present invention to provide a process for preparing said novel metallocenes and to provide a process for polymerization of the xcex1-olefins by means of said metallocenes.
The invention is thus related to novel metallocenes represented by the general formula (I) 
wherein
M represents a transition metal selected from Ti, Zr and Hf,
X and Xxe2x80x2 represent a halogen atom,
R1, R2, R3 represent an alkyl group containing 1 or 2 carbon atoms or a hydrogen atom, providing that at least two of R1, R2, R3 are alkyl groups, and
R4 and R5 represent an alkyl or aryl group containing from 1 to 10 carbon atoms.
The invention also relates to a process for the preparation of metallocenes represented by the general formula (I) comprising the following steps:
a) production of (substituted indenyl)-alkyl(or aryl)-chlorosilane starting from (substituted indenyl)lithium and dichloro-dialkyl(or diaryl)silane,
b) production of (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)silane from the compound obtained in step (a) and fluorenyllithium,
c) production of the dilithium salt of (9-fluorenyl) (1-substituted indenyl)-dialkyl(or diaryl)silane precursor and
d) production of the metallocene by reacting the said dilithium salt with a halide of one of the transition metals mentioned hereabove.
Finally the present invention relates to a process for polymerization of xcex1-olefins by means of said metallocenes.
According to a first aspect, the present invention relates to novel metallocenes of the above general formula (I).
Preferably the transition metal is selected from hafnium and zirconium. Most preferably the transition metal is zirconium.
The halogen atoms X and Xxe2x80x2 are preferably chlorine or bromine atoms and most preferably they are both chlorine atoms.
The groups R1, R2, R3 represent preferably a methyl group or a hydrogen atom, providing that at least two of R1, R2, R3 are methyl groups.
The groups R4 and R5 are preferably alkyl groups and more particularly alkyl groups containing from 1 to 3 carbon atoms.
The most preferred metallocenes according to the present invention are dimethylsilylene (9-fluorenyl)-1-(2,4,7-trimethyl)indenyl zirconium dichloride, dimethylsilylene (9-fluorenyl)-1-(2,4-dimethyl)indenyl zirconium dichloride or dimethylsilylene (9-fluorenyl)-1-(4,7-dimethyl)indenyl zirconium dichloride.
When used in combination with a cocatalyst, such as for example aluminoxane, said novel metallocenes are able to produce polypropylene and more particularly polyethylene with high molecular weight.
According to a second aspect, the present invention relates to a process for producing the novel metallocenes of general formula (I).
The said process comprises the following steps:
a) reacting dichloro-dialkyl(or diaryl)silane with (substituted indenyl)lithium to produce (substituted indenyl)-dialkyl(or diaryl)-chlorosilane,
b) reacting said chlorosilane with fluorenyllithium to produce the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor,
c) reacting said (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor with butyllithium to produce its dilithium salt, and
d) reacting said dilithium salt with a transition metal halide selected from halides of Ti, Zr and Hf to produce the metallocenes.
Preferably, step (a) is carried out with an excess of the chlorosilane. More preferably the (substituted indenyl)lithium is reacted with about two molar equivalents of the silane.
Preferably, step (b) is carried out by reacting the fluorenyllithium with the chlorosilane in equimolar quantity.
Preferably, step (c) is carried with at least two molar equivalents of butyllithium per mole of the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor. Step (d) is most often carried out by reacting the dilithium salt with one equivalent of transition metal halide.
Preferably, reaction step (a) is carried out in an inert solvent, for example an ether. Reaction step (a) is usually carried out at a temperature in the range of about 0xc2x0 C. to about room temperature. At the end of reaction of step (a), the solvent and the excess of dichloro-dialkyl(or aryl)-silane are generally removed in order to separate the produced substituted indenyl-alkyl(or aryl)-chlorosilanes which are oils.
Preferably, the step (b) is carried out in the above-mentioned inert solvent, most often about room temperature. At the end of reaction, the suspension is usually hydrolyzed and the organic phase is isolated. After removal of the solvent, the (9-fluorenyl)-1-(substituted indenyl)-dialkyl(or diaryl)-silane precursor is isolated.
Preferably, step (c) is carried out in an inert solvent, such as toluene or an ether, often under the reflux of said solvent. The resulting Li salt is advantageously separated from the solvent and washed prior to being reacted, in step (d), with about one equivalent of a transition metal halide selected from halides of Ti, Zr and Hf.
Step (d) is preferably carried out in an inert solvent, such as toluene or an ether, often under the reflux of said solvent. After removal of the solvent, the solid metallocene is isolated.
The novel metallocenes according to the present invention are useful as catalysts for the polymerization of xcex1-olefins. The reaction is carried out by contacting said xcex1-olefins with the said metallocene under polymerization conditions. It can be carried out in solution or in suspension in an hydrocarbon diluent or in suspension in one of the monomers maintained in the liquid form or in the gas phase. The polymerization conditions are well known by persons skilled in the art.
The metallocenes according to the invention can be used in combination with one another. They can also be used in combination with aluminoxanes. Methylaluminoxane is preferred. They can also be used in combination with an ionizing agent. This ionizing agent can be chosen from the compounds comprising a first part which has the properties of a Lewis acid and which is capable of ionizing the metallocene and a second part that is inert towards the ionized metallocene. Examples of ionizing agents are triphenylcarbenium tetrakis(pentafluorophenyl)borate, N,Nxe2x80x2-dimethylanilinium tetrakis(pentafluorophenyl)borate, tri(n-butyl)ammonium tetrakis(pentafluorophenyl)borate, tri(pentafluorophenyl)boron, triphenylboron,trimethylboron, tri(trimethylsilyl)borate and organoboroxines.
Organometallic compounds are generally used as cocatalysts and/or poison scavengers. They can be selected from organometallic compounds of lithium, magnesium, zinc, aluminium or tin. The best results are obtained with organoaluminium compounds and in particular with trialkylaluminium compounds.
The olefins can be chosen from those containing up to 20, preferably up to 12 carbon atoms per molecule. The olefin is preferably ethylene or propylene. The metallocenes according to the present invention may be used for the homopolymerization of one of these olefins or for the copolymerizationxe2x80x94random or block copolymerizationxe2x80x94of one of these olefins with one or more comonomers. The preferred comonomers of ethylene are butene, hexene and their mixtures. The preferred comonomers of propylene are ethylene, butene and their mixtures.
The novel metallocenes according to the invention are especially well adapted to the polymerization of ethylene in order to produce with a particularly high activity a polyethylene having high molecular weight. The metallocenes according to the invention are furthermore well suited for obtaining linear polyethylene, i.e. polyethylene whose NMR 13C spectra shows substantially no branching. Polyethylenes having high melting point are advantageously obtained.
In addition to the foregoing description of the invention, the following examples are provided to illustrate the present invention.
In these examples reactions are carried out under an argon atmosphere using standard Schlenk, techniques. Toluene, diethyl ether, tetrahydrofuran (THF) and pentane were distilled from Na/K alloy under argon. Dichloromethane was distilled from CaH2 under argon.
Melting points of the polymers were determined by DSC with a Perkin-Elmer DSC-System. 13C NMR spectra were determined on DPX300/AMX500 spectrometers in CDCl3 at room temperature, and at 80xc2x0 C. in C6D5Cl. 1H NMR spectra were recorded on a AC-200 spectrometer.
1. Preparation of Metallocenes